<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>抽象画布可视化</title>
<style>
body {
  background: #000;
  overflow: hidden;
}
canvas {
  display: block;	
  left: 50%;
  margin: -200px 0 0 -200px;
  position: absolute;
  top: 50%;
}
</style>
</head>
<body>
<canvas id="canvas" width="400" height="400"></canvas>
<script>
var smoothTrail = function(c, cw, ch){
  this.init = function(){
    this.loop();
  };		
  var _this = this;
  this.c = c;
  this.ctx = c.getContext('2d');
  this.cw = cw;
  this.ch = ch;
  this.mx = 0;
  this.my = 0;
  this.trail = [];
  this.maxTrail = 200;
  this.mouseDown = false;
  this.ctx.lineWidth = .1;
  this.ctx.lineJoin = 'round';
  this.radius = 1;
  this.speed = 0.4;
  this.angle = 0;
  this.arcx = 0;
  this.arcy = 0;
  this.growRadius = true;
  this.seconds = 0;
  this.milliseconds = 0;
  this.rand = function(rMi, rMa){return ~~((Math.random()*(rMa-rMi+1))+rMi);};
  this.hitTest = function(x1, y1, w1, h1, x2, y2, w2, h2){return !(x1 + w1 < x2 || x2 + w2 < x1 || y1 + h1 < y2 || y2 + h2 < y1);};
  this.createPoint = function(x, y){
    this.trail.push({
      x: x,
      y: y						
    });
  };
  this.updateTrail = function(){
    if(this.trail.length < this.maxTrail){
      this.createPoint(this.arcx, this.arcy);
    }					
    if(this.trail.length >= this.maxTrail){
      this.trail.splice(0, 1);
    }					
  };
  this.updateArc = function(){
    this.arcx = (this.cw/2) + Math.sin(this.angle) * this.radius;
    this.arcy = (this.ch/2) + Math.cos(this.angle) * this.radius;					
    var d = new Date();
    this.seconds = d.getSeconds();
    this.milliseconds = d.getMilliseconds();
    this.angle += this.speed*(this.seconds+1+(this.milliseconds/1000));
    if(this.radius <= 1){
      this.growRadius = true;
    } 
    if(this.radius >= 200){
      this.growRadius = false;
    }
    if(this.growRadius){
      this.radius += 1;	
    } else {
      this.radius -= 1;	
    }
  };
  this.renderTrail = function(){
    var i = this.trail.length;					
    this.ctx.beginPath();
    while(i--){
      var point = this.trail[i];
      var nextPoint = (i == this.trail.length) ? this.trail[i+1] : this.trail[i];
      var c = (point.x + nextPoint.x) / 2;
      var d = (point.y + nextPoint.y) / 2;						
      this.ctx.quadraticCurveTo(Math.round(this.arcx), Math.round(this.arcy), c, d);
    };
    this.ctx.strokeStyle = 'hsla('+this.rand(170,300)+', 100%, '+this.rand(50, 75)+'%, 1)';	
    this.ctx.stroke();
    this.ctx.closePath();
  };
  this.clearCanvas = function(){
    this.ctx.globalCompositeOperation = 'destination-out';
    this.ctx.fillStyle = 'rgba(0,0,0,.1)';
    this.ctx.fillRect(0,0,this.cw,this.ch);					
    this.ctx.globalCompositeOperation = 'lighter';
  };
  this.loop = function(){
    var loopIt = function(){
      requestAnimationFrame(loopIt, _this.c);
      _this.clearCanvas();
      _this.updateArc();
      _this.updateTrail();
      _this.renderTrail();							
    };
    loopIt();					
  };
};
var isCanvasSupported = function(){
  var elem = document.createElement('canvas');
  return !!(elem.getContext && elem.getContext('2d'));
};
var setupRAF = function(){
  var lastTime = 0;
  var vendors = ['ms', 'moz', 'webkit', 'o'];
  for(var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x){
    window.requestAnimationFrame = window[vendors[x]+'RequestAnimationFrame'];
    window.cancelAnimationFrame = window[vendors[x]+'CancelAnimationFrame'] || window[vendors[x]+'CancelRequestAnimationFrame'];
  };
  if(!window.requestAnimationFrame){
    window.requestAnimationFrame = function(callback, element){
      var currTime = new Date().getTime();
      var timeToCall = Math.max(0, 16 - (currTime - lastTime));
      var id = window.setTimeout(function() { callback(currTime + timeToCall); }, timeToCall);
      lastTime = currTime + timeToCall;
      return id;
    };
  };
  if (!window.cancelAnimationFrame){
    window.cancelAnimationFrame = function(id){
      clearTimeout(id);
    };
  };
};
  if(isCanvasSupported){
    var c = document.createElement('canvas');
    c.width = 400;
    c.height = 400;			
    var cw = c.width;
    var ch = c.height;	
    document.body.appendChild(c);	
    var cl = new smoothTrail(c, cw, ch);				
    setupRAF();
    cl.init();
  }
</script>
</body>
</html>